When you have an endoscopy done, what does the doctor look for and sees?

Anything abnormal: In an endoscopy, a medical device is passed into the body (through mouth or anus depending upon 'upper' or 'lower' approach). The doctor driving the scope can see the lining of the gastrointestinal system and can detect abnormalities such as ulcers, infections, strictures, polyps, tumors, etc... These can be photographed / biopsied / cultured / etc..., allowing specific diagnoses.